Lowpass filters are commonly utilized in channel estimation to suppress high frequency estimation error components. In most wireless communication systems, pilot signals are transmitted to facilitate channel estimation at the receiver. Each pilot symbol provides an estimate of the channel impulse response. The rate of pilot symbols has to be sufficiently high so that variations of the channel impulse response can be tracked even at high speeds. This implies that the rate of pilot symbols by far exceeds the rate of channel variations at lower speeds. It can be assumed that the channel estimation errors are zero-mean and uncorrelated for different pilot symbols. High frequency error components can be effectively suppressed by averaging the channel impulse response estimates from several pilot symbols, i.e. by applying lowpass filtering. However, this lowpass filter introduces a group delay, which results in substantial systematic channel estimation errors. FIG. 1 illustrates the time response of an exemplary channel coefficient 104 and the lowpass filtered channel coefficient 102. 104 denotes an exemplary realization of h(k), 102 denotes an exemplary realization of h(k) and k stands for the pilot symbol index.
There is a need to mitigate systematic channel estimation errors due to group delay of lowpass filtering.